Portion of a heat sink



FIG. 1 is a top perspective view of the new design for a portion of a heat sink as seen from the front, top;

FIG. 2 is a top plan view thereof;

FIG. 3 is a bottom plan view thereof;

FIG. 4 is a front elevational view thereof;

FIG. 5 is a rear elevational view thereof;

FIG. 6 is a right side elevational view thereof, the opposite side view being a mirror image thereof; and,

FIG. 7 is a bottom perspective view thereof.

The broken line disclosure is for environmental purposes only and does not form a part of the claimed design. 

CLAIM The ornamental design for a portion of a heat sink, as shown and described. 